Post navigation

A New Tender Drawbar for a Marklin 4-6-2

As promised in last week’s post, this week I have a replacement part for a German steam engine to share with you.

The engine is a Class BR03 4-6-2 built for the DB (Deutsche Bahn – National Railway of Germany). The model is HO scale and made by Marklin.

As well as converting this loco to DCC it also needed a few repairs, including a replacement tender drawbar. The tender houses the motor which drives two of the four axles. The locomotive is free-rolling but has a very heavy weight in the boiler. This not only keeps it on the track at speed but also helps with power pickup as the tender wheels all have traction tires.

In order to keep the coupling between the locomotive and tender close but smooth Marklin have devised a drawbar which incorporates springs. Below you can see what is left of the original drawbar. The metal springs clip into the slots in the tails and a screw runs through the loop. This system absorbs any bounce, keeping the locomotive running smoothly, and allows great flexibility.

However, as you can see below, the drawbar has suffered a lot of damage, which is not fixable by simply gluing it back together as there are bits missing.

This is a perfect situation for a 3D printed part and that is exactly what I’m going to do. As this part needs to be strong but detailed, to get the slots on the right place, I’ll be using Shapeways’ Frosted Ultra Detail material, which has proved itself time and time again as being ideal for this sort of job. You may recall back in December of 2015 I used this material for a set of replacement gears in an O scale Rivarossi F9, which you can read about here. The gears needed to be precise and strong, as the forces passing through them had already cracked the original injection moulded gears. The FUD is a hard acrylic material which gives it its strength and as it’s printed to a 29 micron layer thickness, the detail is very precise.

As always it starts with a 3D drawing of the part. Great care was taken to capture all the lumps and bumps on the original so it’ll be a good fit.

To ensure the part is the right shape, as well as measuring it, I scanned the original on a photocopier and brought that image into my drawing package. I could then lay the new part over the top as a final check.

This drawbar is currently being printed by Shapeways, along with the steps from last week and several other new parts. They are due to arrive in the next two weeks, when they do I will share the fitting of the drawbar with you.

In the meantime next week I have another new 3D printed part to share; this time it’s for a OO scale English signal box.